Ctenophora

Eschscholtz, 1829

comb jellies, sea gooseberries, sea walnuts, Venus's girdles

Species Guides

Ctenophora is a of marine distinguished by eight rows of cilia used for locomotion, called comb rows. They are the largest animals to swim using cilia. Unlike cnidarians, they lack stinging and instead capture prey using colloblasts—sticky adhesive cells. The phylum contains approximately 150–186 recognized exhibiting diverse body plans, from -shaped cydippids with retractable tentacles to flattened benthic platyctenids and large-mouthed beroids. Ctenophores possess a decentralized nerve net without a brain, and their phylogenetic position as either the earliest or second-earliest branching animal lineage remains actively debated.

Pronunciation

How to pronounce Ctenophora: /ktɛˈnɒfərə/

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Identification

Distinguished from all other animals by colloblasts—specialized sticky used to capture prey. Eight comb rows bearing bands of cilia (ctenes) run meridionally from aboral to oral pole, creating iridescent rainbow effects when beating. Body consists of a gelatinous mesoglea sandwiched between two cell layers; lacks the cnidocytes (stinging cells) characteristic of cnidarians. Most exhibit biradial or rotational symmetry rather than true radial symmetry. Statocyst at aboral pole provides balance sensing.

Habitat

Exclusively marine; found from polar waters at −2°C to tropical waters at 30°C. Occurs from surface waters to depths exceeding 7,000 meters. Coastal withstand wave action and sediment; oceanic species often extremely fragile and difficult to capture intact. Benthic forms (order Platyctenida) attach to substrates; planktonic forms dominate open water.

Distribution

Worldwide in marine environments across all ocean basins. Accidentally introduced to inland saline lakes in Egypt (Birket Qarun, El Rayan II) via fish transport in 2013–2014. established in Black Sea, Sea of Azov, Caspian Sea, eastern Mediterranean, North Sea, and Baltic Sea through ballast water transport, primarily of Mnemiopsis leidyi.

Diet

Almost exclusively predatory. Prey ranges from microscopic larvae and rotifers to small crustaceans including copepods, amphipods, and krill. Some specialize: Beroe preys mainly on other ctenophores; Lampea feeds exclusively on salps; Haeckelia consumes jellyfish and incorporates prey's nematocysts into its own tentacles. Juveniles of two Lampea species are parasitic on salps. Can consume up to ten times body weight daily when food is abundant.

Life Cycle

Development is direct with no ; juveniles generally resemble miniature . Most are simultaneous or sequential with external ; at least three species have separate sexes (dioecy). Platyctenids reproduce asexually by cloning. Members of Lobata and Cydippida exhibit dissogeny—two sexually mature stages, first as larvae and later as juveniles/adults. Mnemiopsis leidyi can revert to cydippid stage under environmental stress. Adults can regenerate damaged tissues.

Behavior

Locomotion powered by beating of comb rows, normally with mouth leading; can reverse direction. Diel feeding patterns observed in some driven by prey field composition. Some species hang motionless using tentacles as passive capture webs; others are active ambush . When disturbed, some species (Bathyctena chuni, Euplokamis stationis, Eurhamphaea vexilligera) secrete ink. produced by photocytes in meridional canals, typically blue or green.

Ecological Role

Significant in marine , potentially controlling copepod and preventing overgrazing of phytoplankton. Mnemiopsis leidyi caused fishery collapses in the Black Sea and Sea of Azov through on fish larvae and zooplankton. Serve as prey for jellyfish, sea turtles, chum salmon, and other fish. May balance by regulating microplankton populations; high reproductive capacity enables rapid population increases.

Human Relevance

Mnemiopsis leidyi has caused substantial economic damage to fisheries in the Black Sea, Sea of Azov, and Caspian Sea. Control efforts include introduction of predatory ctenophore Beroe ovata. Some studied as models for developmental , neurobiology, and evolutionary origins of animals due to their simple and disputed phylogenetic position. studied for potential applications. Occasionally encountered in public aquarium displays.

Similar Taxa

CnidariaSuperficially similar gelatinous marine with radial symmetry and tentacles, but cnidarians possess stinging cnidocytes whereas ctenophores use adhesive colloblasts; ctenophores have biradial symmetry and eight comb rows absent in cnidarians.
PoriferaBoth lack true brains and centralized , but sponges are filter-feeders with no ciliary locomotion or comb rows; ctenophores are active with distinct body axis and specialized swimming structures.